PROJECT SUMMARY/ABSTRACT Therapeutic interventions that target fundamental mechanisms of aging are being sought to radically transform public health. Indicators of biological aging that can be identified prior to overt manifestations of late-life conditions, and concomitantly serve as predictors of future health and longevity, could facilitate this effort. As highlighted in this RFA, resilience, defined as the ability of an organism to adequately respond to physical challenges, may offer one such opportunity. Thus, the objective of this proposal is to develop and validate a battery of disease-agnostic physical challenges to enable the evaluation of resiliency in mice. To this end, in Specific Aim 1 we will determine which physical challenges best reveal differences in resilience between and within younger, middle-aged, and older mice. Specifically, we will assess acute responses to anesthesia, chemotherapy, surgery, and dehydration in cohorts of 4-month-old, 12-month-old, and 20-month-old mice. In Specific Aim 2, using the physical challenges deemed optimal in Specific Aim 1, we will determine the extent to which baseline resilience of middle-aged mice longitudinally predicts healthspan using discriminating measures of physical, metabolic, cardiovascular, and immune function at Mayo Clinic, and lifespan at the University of Michigan. Given the considerable evidence that aberrant mTOR signaling and senescent cell accumulation are mediators of aging, in Specific Aim 3 we will determine the extent to which rapamycin and targeted clearance of p16INK4a-positive senescent cells affect the resilience of older mice to physical challenges. We expect that a standardized battery of clinically relevant measures of resilience in laboratory mice will provide a new framework in which to test innovative and potentially transformative interventions to promote healthy aging. In humans, the emergence of chronic diseases and syndromes such as frailty may reflect a point of no return. Compromised resilience earlier in life, on the other hand, may ultimately serve as a therapeutic opportunity in which the progression of aging-related molecular and cellular damage can be attenuated, if not reversed.